US 3815120 A
An electronic driver circuit for a time-multiplex operated gaseous indicator display comprising a plurality of indicator tubes each including two or more cathode arrays for selectively presenting any one of several characters at each array position by establishing an ionizing potential difference between one or more cathodes of each array and its associated anode. The anodes of each tube are connected in parallel and anode excitation is applied to the individual tubes sequentially at a predetermined repetition rate. Corresponding cathodes of similar character positions in each tube are also connected in parallel and cathode drivers coupled thereto are also rendered effective sequentially whereby a desired character is energized at each position during the interval in which anode excitation is applied thereto concurrently with activation of the associated cathodes, the rate of anode sequencing being rapid enough to provide continuous presentation of the selected characters.
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Description (OCR text may contain errors)
United States Patent [191 Kanda [451 June 4, 1974 GAS DISCHARGE DISPLAY APPARATUS HAVING TIME MULTIPLEX OPERATED ANODE AND CATIIODE DRIVER CIRCUITS  Inventor: Alvin F. Kanda, Scottsdale, Ariz.
[ 73] Assignee: Sperry Rand Corporation,
 Filed: July 7, 1972  Appl. No.1 269,681
 US. Cl. 340/336, 340/324 M, 340/343  Int. Cl. G09f 9/32  Field of Search 340/324 R, 336, 324 M,
 References Cited UNITED STATES PATENTS 3,307,171 '2/1967 Claessen 340/324 R 3,354,342 11/1967 Ohntrue et al.... 340/324 R 3,395,268 7/1968 Barton 340/324 R 3,555,544 1/1971 Atkins. 340/336 3,614,771 10/1971 Band et al 340/336 7/1972 Nakada et al 340/336 RIVERS Primary Examiner.l0hn W. Caldwell Assistant ExaminerMarshall M. Curtis Attorney, Agent, or FirmJames M. Thomson; R. .1.
Steinmeyer 5 7 ABSTRACT sponding cathodes of similar character positions in each tube are also connected in parallel and cathode drivers coupled thereto are also rendered effective sequentially whereby a desired character is energized at each position during the interval in which anode excitation is applied thereto concurrently 'with activation of the associated cathodes, the rate of anode sequencing being rapid enough to provide continuous presentation of the selected characters.
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: A I E A l a n l CATH H DRIVER 1 d DECODER CATH l 1401- DRIVER I CATH g DRIVER 1417" q f e d i I TO I CATHODE DRIVERS 182 H 15 EVEN f DlGlT SWITCH TIMING CONTROL To ANODE DRIVERS PATENTEDJUH 4 I974 ANODE DRIVER SHEET 20F 4 ANODE DRIVER DlGlT SWITCH GAS DISCHARGE DISPLAY APPARATUS HAVING TIME MULTIPLEX OPERATED ANODE AND CATIIODE DRIVER CIRCUITS BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates to a novel time multiplex driver circuit for a multi-character cold cathode negative glow type gaseous discharge display device.
2. Description of the Prior Art A cold cathode negative glow type gaseous discharge display tube typically comprises a hermetically sealed enclosure containing an ionizable gas at suitable pressure and respective anode and cathode electrodes disposed in the gas in relatively close spacing to one another. Either alternating or direct current electrical 'excitation may be used for operation of the tube. ln the case of direct current excitation, for example, application of an ionizing potential difference between an anode and cathode produces visible glow in a thin layer of the gas proximate and generally configured to the shape of the cathode which may be in the form of letters, nume'ralsor other symbols desired to be displayed. Versatility of character display has been achieved by the development of tubes containing a plurality of individually shaped cathodes aligned one in back of the other in a stack along the direction of normal viewing or alternatively containing a plurality of cathode segments arranged in a suitable alphanumeric format. A desired character is displayed with the shaped cathode stack by establishing an ionizing potential difference between the anode and the appropriate cathode. In a tube having a segmented cathode array, on the other hand, a desired character is displayed by providing the required ionizing potential between the anode and each of an appropriate. combination of cathode segments which together form the desired character.
Simultaneous presentation of multiple characters can be produced with either the stack or segmented array type tubes by using a plurality of either of such tubes disposed, for instance, in side by side relation so that a distinct character can be displayed at the location of each stack or segmented array. One way in which such an arrangement of tubes may be activated is to connect all the anodes in parallel and connect each stack or segmented array to a separate cathode driver. The individual cathode drivers typically include suitable logic and switching circuits for selecting the'individual shaped cathodes or cathode segments as the case may be. For a multi-character display, however, such as a multidigit number, it is apparent that the number of cathode drivers becomes quite large with this kind of driver arrangement. ln the interest of reducing the complexity and cost of the driver circuits, there have been developed heretofore anode strobing or time multiplexing techniques in which common cathodes of each stack or segmented array are connected in parallel and activated from a single cathode driver circuit, while the anodes of the respective stacks or arrays are energized sequentially. As each anode is energized, a character is produced in the associated stack or array in accordance with the cathode or segments which are activated at the same time. The anode strobing rate is made sufficiently fast commensurate with persistence of the ionized glow, and vision of the human eye so that all of the characters appear to be continuously energized without perceptible flicker.
Although a significant reduction of driver circuitry is realized by means of anode strobing in the foregoing manner, other problems arise as a consequence of the strobing when used with tubes which contain more than one stack or array of cathodes. Segmented array type tubes in particular are customarily constructed with two, three or more arrays for the purpose of displaying multiple digit numbers. It has been found that when two or more arrays are located in a single gas enclosure, it is necessary to use a blanking interval between energization of successive anodes and/or cathodes to preclude the occurrence of an inter-digit positiveglow column along with the negative glow at the individual digit positions. lnasmuch as the brightness of a display is directly related to the on-time or duration of the time interval that each anode and its associated cathodes are concurrently activated, it will be appreciated that each character mustbe energized for at least a prescribed minimum time to obtain a certain luminous intensity. The required on-time for each character in turn limits the number of characters which can be displayed for a given repetition rate, that is rate of successively energizing a discrete character of a multi-character display. The necessity for a blanking interval further limits the maximum number of characters which can be displayed for a prescribed brightness and repetition rate. For example, assume that an on-time of 200 milliseconds is required to achieve desired brightness and that a blanking interval of 50 milliseconds is required to preclude inter-digit glow. To satisfy these conditions in conjunction with a repetition rate of energization once per second, the number of characters which can be simultaneously displayed is limited to a maximum of four. lf blanking was not required, however, a total of five characters could be displayed under the same operating conditions.
It is a principal object of the present invention to provide a novel character display time multiplexing driver circuit which obviates the need for blanking intermediate activation of successive character electrodes whereby the display brightness may be enhanced and the number of characters displayed may be maximized in accordance with a predetermined rate of repetitive energization of the discrete characters to assure presentation without flicker. Although apparatus constructed in accordance with the principles of the present invention is superior insofar as these qualities are concerned relative to the aforedescribed prior art strobing technique, it should be recognized, as will become apparent from a reading of the detailed description provided hereinafter, that the inventive apparatus is in fact more costly in the case of displays consisting of only a few characters. Economic benefits from the viewpoint of low cost are obtained, however, in addition to the above-mentioned advantages, when the display consists of several or more characters, the cost cross-over of the prior art and present inventive techniques being dependent on the relative cost of the anode and cathode activating elements and the number of characters per tube.
SUMMARY OF THE INVENTION In accordance with the principles of the present invention, a multi-character display is provided in a typical embodiment by the use of a plurality of indicator tubes each containing two anodes operatively associated with respective segmented cathode arrays. The
anodes of each tube are connected in parallel for simultaneous electrical excitation sequentially with all of the other tubes. In other words, first the anodes of tube 1 are simultaneously energized then the anodes of tube 2, and so on, until all the tube anodes are energized and then the cycle repeats for as long as the characters are to be displayed. In the case of the cathodes, one segmented array of each tube is coupled to one group of cathode drivers while the other segmented array of each tube is coupled to another group of cathode drivers. The respective groups of cathode drivers are rendered operative alternately as a result of which during the interval that the anodes of each tube are energized an ionized glow display will be produced in succession at the respective segmented array positions of each tube, the shape of the glow being dependent on the cathode selected to be activated. In'other words. during a first time interval in which the anodes of tube 1 are energized, an ionization condition will be produced at one segmented array in one half of the time interval and at the other segmented array in the other half of the time interval and so on for each tube as its anodes are energized in sequence. As previously mentioned, the repetition rate is made fast enough to provide for continuous presentation of all the characters of the display.
From a reading of the following description of the preferred embodiments, it will be understood more fully that the multiplexing technique of the present invention is principally adapted for use in applications where each tube has at least two segmented arrays or groups of cathodes and associated anodes but is not limited to any particular number of arrays or anodes.
BRIEF DESCRIPTION OF THE DRAWINGS The preferred embodiments of the invention will be described with reference to the appended drawings. wherein: 1
FIGS. la and 1b are a schematic diagram illustrating a driver-circuit of the present invention interconnected with a plurality of gas discharge indicator tubes each containing two segmented cathode arrays and associated anodes.
FIGS. 2a 2lz are timing diagrams depicting waveforms useful in explainingthe operation of the circuit of FIG. 1.
FIG. 3 is a block diagram of a cathode driver circuit incorporating a latching feature which may be used in the apparatus of FIG. 1 for further enhancement of the display brightness.
FIGS. 4a-4f are timing diagrams depicting waveforms useful in explaining the operation of the apparatus of FIG. 1 when constructed with a cathode driver as shown in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the driver circuit of the present invention will be described with regard to display apparatus including a plurality of cold cathode negative glow gaseous discharge indicator-tubes a, 10b NM. The respective tubes are essentially identical in construction and typically comprise a hermetically sealed enclosure containing an ionizable gas at suitable pressure and formed at least in part of a transparent material to enable viewing of the characters disposed which is to be displayed, the numbers of tube ltla' representing the two least significant digits, and those of tube lOn representing the two most significant digits of the displayed number. More specifically, as indicated with reference to tube 10a, each tube contains a pair of anodes 11a, 11a" and respective associated groups of cathodes 12a, 12a, the individual cathodes of each group are further designated with the letters a-g. Respective anode drivers 13a. 13b l3n are coupled to the anodes of the individual tubes 10a, 10b in. As illustrated by anode driver 130, each such driver includes a pnp transistor having its emitter connected to the positive terminal of a voltage source 8+ and its collector connected in parallel to the anodes of the associated indicator tube. First and second groups playing the desired number at each digit position. Each group of cathode drivers has seven output leads also designated by the letters a-g for coupling to the correspondingly designated cathode segments of the cathode arrays in such a way that the output leads of driver group 14' connect to the least significant digit cathode group l2a, to cathode group 12b of tube 10b and so on to alternate groups of cathodes so as to be connected finally to'cathode group 12n' of tube l0n. Likewise, the output leads of driver group 14" connect to the next to least significant digit cathode group 12a of tube 10a to cathode group 12b of tube 10b and soon to alternate cathode groups so as to be connected finally to cathode group 12):" of tube ltln. As illustrated by cathode driver element l4'a of driver group 14', each such driver element comprises an npn transistor having its collector connected to an individual output lead of the driver group in which it is incorporated whileits emitter is coupled through a resistor to the collector of an npn transistor comprising odddigit switch 15', the emitter of the latter in turn being connected to ground 16. The driver elements of driver group 14 are similarly constructed and each in turn connected to an even-digit switch 15" which is also returned to ground ll6.
The operation of the display apparatus will now be described with reference to the waveforms of FIGS. 2a-2h. As previously explained, the general idea is to strobe or sequentially energize the respective anodes and at the same time activatethe appropriate associated cathode segments. For simplicity of description, assume that all anodes are initially de-energized, a condition which is obtained by holding the base of the transistors of the respective anode drivers 13a to l3n at a potential approximately equal to or slightly more posi tive than the B+ potential connected to the emitter of each anode driver. Thereafteneach anode driver can be repetitively activated in sequence proceeding, for example, from the least to the most significant digits. Thus in a first time interval t, of the repetition period T, the potential at the base of anode driver 13a is driven slightly negative with regard to its emitter to switch the transistor into an on or saturated state as indicated by the waveform of FIG. 2a and thereby connect the B+ supply directly to the anode of tube 10a. Likewise, in time interval immediately following in terval t anode driver 13b is switched to an on condition as indicated inFIG. 2b to apply the B+ to the anodes of tube b and so on in succeeding time intervals until finally the 8+ is applied to tube lOn through anode driver l3n switched to an on condition in interval t,, as illustrated in FIG. 2c, after which the cycle repeats continuously for as long as it is desired to display the multi-digit number.
The operation with respect to the individual tubes in each of the intervals t, to I is essentially the same. Consider in further detail the nature of the operation in time interval and the first half of interval in other words, with respect to the three least significant digits for the purpose of displaying, for example, the number 717. In the first half of time interval r,, the group of cathode activating elements 14' activates the appropriate cathodes of cathode group 12a to display the least significant digit. Since numeral 7 is to be displayed at this position, cathodes a, b and c of cathode group 12a are activated to produce an ionizing potential difference between anode 11a and the activated cathodes. At the same time, of course, the corresponding cathodes a, b, c of the alternate cathode groups 12b through l2n are also activated, but this is of no consequence since the associated anodes are not energized during interval As in the case of the anode drivers, all of the cathode driver elements of driver groups 14 and 14" and the odd and even-digit switches 15' and 15", may be assumed to be held initially in an off or deenergized condition. During the first half of time interval 1,, however, the potential on the base of the transistor of odd-digit switch 15' is driven slightly-positive relative to ground to drive switch l5'into an on or satu rated state as illustrated in FIG. 2d so that its collector is essentially connected to ground and at the same time the potential applied to the base of the transistors of cathode driver elements 14a, 14b, 140' is driven positive to turn these drivers on as indicated in FIGS. 2f, 2g and 2b to operate in an unsaturated current-limited mode so that the related cathodes (a, b, c of cathode group 12a.) are held close to ground potential. In the second half of time interval odd-digit switch 15 is reversed to an off condition and simultaneously evendigit switch 15" is driven into an on condition as indicated in FIG. 2e. Since numeral 1 is to be energized at the next to leastsignificant digit position, the appropriate cathode driver elements of driver group 14" are energized as explained with reference to driver group 14 to hold cathode segments b and c of cathode group 12a close to ground potential, through the energized cathode driver elements of driver-group l4" and evendigit switch 15". simultaneously with the application of the B+ potential to anode 11a. At this time, cathode driver element 14a is not energied so that numeral 1 is displayed in the next to least significant digit position alongside numeral 7 in the least significant digit position.
At the start of the next time interval t commencing at the termination of interval I the potential at the base of the transistor of anode driver 13a reverts to its original level thereby returning driver 13a to an off condition and removing the B+ from the anodes of tube 10a. At the same time, anode driver 13b is switched to an on condition to apply the B+ potential to the anodes of tube 10b. As in the case of the operation of tube 10a,
during the first half of interval odd-digit switch 15' is on and even-digit switch 15" is off whereby the oath ode driver elements of driver group 14" are rendered ineffective and those of driver group 14' again become effective for energizing cathodes a, b, c of cathode group 12b in tube 10b so that numeral 7 is displayed at the third least significant digit position. It should now be apparent that no inter-digit glow will occur inasmuch as the anode potential is the same between anodes 11a and 11a and because of physical isolation between cathode groups and 12b".
The control signals applied to the base terminals of the cathode drivers are obtained from a conventional binary coded decimal to seven segment decoder 17 which receives four-wire input bits A, B, C, D in the standard format 0001, 0010, 0011, 0l00, etc., for the purpose of selecting the correct cathode segments to display any one of the numerals 0 to 9 in each digit position. The decoder is synchronized with the on-off controlsignal applied to the anode drivers and the odd and even-digit switches by means of clock pulses obtained from timing control unit 18. Units 17 and 18 may be an integral part of a system such as a calculator, clock or counter.
An alternative cathode driver configuration which may be used in combination with the indicator tubes, anode drivers and timingcontrol unit of FIG. I is shown in FIG. 3. This cathode driver configuration incorporates a latching feature which necessitates the use of a pair of binary coded decimal-to-seven-segment decoders 27', 27" coupled respectively to latching circuits 28 28''. The circuit is thus more expensive than the one previously described, but offers the advantage of enhanced brightness in view of the fact that the cathode segmentsof each array may be held in an activated state for essentially the full duration of the respective timing intervals t, through 1,, rather than for only half of each interval. This will be understood more fully from a reading of the following description given with reference to FIGS. 4a through 4f. As explained in connection with the description of the apparatus of FIG. 1, each anode driver is switched on in succession as indicated in FIGS. 4a and 4b. Thus, the B+ potential is coupled to tube 10a in time interval t The least significant digit information (FIG. 4/) is applied to the pair of latch cicuits 28', 28" near the end of the preceding (n"') time interval. At this time, however, only the odddigit latch 28' is activated as by an odd-digit sample signal (FIG. 4c) supplied from the timing control'unit. Hence, the least significant digit information is stored only in latch circuit 28. In like manner, an even-digit latch signal (FIG. 4d) is applied to even-digit latch circuit 28" to sample the next to least significant digit information near the beginning of interval Similar sampling is performed shortly before the end of each time interval and shortly after the beginning of each succeeding time interval as indicated in FIGS. 4a through 4d. The least significant and next to least significant stored digits are applied to decoders 27' and 27" respectively for energization of the appropriate cathodes of cathode groups 12a and 12a" of tube 10a for the duration of the on-time i of the decoder en abling pulse (FIG. 4e) applied in parallel to both decoders. The sequence of operation continues in the same fashion for the remaining more significant digits. It will be recognized, of course, that a half-interval time lag exists between the arrival of the four-wire data input and the presentation of the corresponding digit information. The repetition rate is sufficiently fast,
however", that for all practical purposes the data is displayed in real time, that is instantaneously as it is received.
Irrespective of whether the director latching type cathode drive of FIGS. 1 and 3, respectively, is used the general operating criteria for the driver configuration of the present invention is that a number of anode drivers equal to the number of'indicator tubes is required while the number of cathode driving elements required is equal to the number of cathode segments per tube with an additional switch being required for each group of cathode drivers. in the case of a three digit tube for example. a separate group of cathode drivers and a related group switch would be required for each digit position.
While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.
1. An electronic driver circuit for a gaseous cold cathode negative glow type display device including a plurality of groups of cathodes and a plurality of anodes wherein each anode is operatively associated with a group of cathodes and the individual cathodes of each group of cathodes are selectively activatable for displaying-desired characters by establishing a suitable potential difference between at least one cathode of each group and its associated anode, said circuit comprising cathode activating means including at least two groups of cathode activating elements, each group of cathode activating elements coupled to at least one distinct group of cathodes for selectively activating the cathodes thereof,
anode driver means coupled to said plurality of anodes for selectively applying electrical excitation in sequence. to respective groups of anodes each group including at least two anodes, and
control means coupled to said cathode activating means for successively and exclusively rendering said groups of cathode activating elements operable concurrently with each sequential energization of each of said groups of anodes so that a desired character is energized at the group of cathodes coupled to the currently operable group of cathodes activating elements and associated with the currently energized group of anodes.
2. The apparatus of claim 1 wherein said groups of cathode activating elements each include a plurality of individual cathode drivers each of which is coupled to a respective cathode of at least one group of cathodes.
3. The apparatus of claim 2 wherein the groups of cathodes are so constructed and arranged and interconnected with the driver circuit that the respective groups of cathode activating elementsare coupled to alternate groups of cathodes.
, 4. A cold cathode negative glow type gaseous character display apparatus comprising means enclosing an ionizable gaseous medium,
a plurality of groups of cathodes and a plurality of anodes, each anode operatively associated with a respective group of cathodes, disposed in said gaseous medium, I
anode driver means coupled to said anodes for selectively applying electrical excitation in sequence to respective groups of anodes each group including at least two anodes,
cathode activating means including at least two groups of cathode activating elements, each group of cathode activating elements coupled to at least one distinct group of cathodes for selectively activating the cathodes thereof wherebydesired characters are displayed by establishing a suitable potential difference between at least one cathode of each group and its associated anode, and
control means coupled to said cathode activating means for sequentially and exclusively rendering said groups of cathode activating elements operable during application of electrical excitation to each group of anodes so that a desired character is energized at a different one of said groups of cathodes in successive time intervals at the group of cathodes coupled to the currently operable group of cathode activating elements and associated with the currently energized group of anodes.
5. The apparatus of claim 4 wherein said groups of cathode activating elements each include a plurality of individual cathode drivers each coupled-to a respective cathode of at least one group of cathodes.
6. The apparatus of claim 5 wherein the groups of cathodes are so constructed and arranged and interconnected with the groups of cathode activating elements that the respective groups of cathode activating elements are coupled to alternate groups of cathodes.
7. The apparatus of claim 5 wherein the enclosing means comprises means forming a plurality of hermetically sealed tubes each including at least two groups of cathodes, one group of cathodes of each tube being connected to a first group of cathode activating elements and another group of cathodes of each tube being connected to a second group of cathode activating elements.
8. The apparatus of claim 5 wherein the enclosing means comprises means forming a plurality of hermetically sealed tubes each including a plurality of cathode groups, each cathode group of the respective tubes being connected toa discrete group of cathode activating elements. i
9. The apparatus of claim 5 wherein each group of cathodes comprises an array of cathode segments arranged in an alphanumeric format whereby desired 1 characters are displayed by activating selected cathode segments of the respective groups of cathodes concurrently with application of electrical excitationto the associated anodes.
10. The apparatus of claim 4 wherein each group of anodes includes the same number of anodes, and the number of groups of cathode activating elements is equal in number to the number of anodes in each anode group.
11. The apparatus of claim 10 wherein the enclosing means comprises means forming a plurality of hermetically sealed tubes each including at least two groups of cathodes,'one group of cathodes of each tube being connected to a first group of cathode activating elements and another group of cathodes of each tube being connected to a second group of cathode activating elements.- 1
y 12. The apparatus of claim 10 wherein 9 10 the enclosing means comprises forming a plurality of each said group of anodes comprises adjacent anhermetically sealed tubes each including a plurality odes, and of cathode groups, each cathode group of the reeach said tube includes one respective group of anspective tubes being connected to a discrete group odes. of cathode activating elements, 5